(a) Field of the Invention
The present invention relates to biodegradable plastic composition. More particularly, it relates to a material composition for plastic molded article, which not only can be molded into various products having good physical properties and safety, but also can minimize the environmental problems of soil, air, and sea pollution caused by burial or incineration of wastes of the product because the inventive material comprises natural materials, i.e., rice powder and/or corn powder, and the waste of the products made from the composition can be degraded by microbes in the natural world after a certain period.
(b) Description of the Related Art
Synthetic polymer represented by plastic is one of materials necessary for convenient and comfortable present-day life along with metal and ceramic. Such synthetic polymer is used for products of various industry fields such as daily life material, construction, medical service, agriculture, etc., and the amount of use is remarkably increasing. However, contrary to natural polymer, most of synthetic polymer is not easily decomposed, so the disposal and management of wastes of synthetic polymer products are big social problems for all the countries over the world.
Such plastic wastes are treated by the conventional methods such as recycling, incineration and burial. But especially, the recycled articles have restrictions in their uses, and have many problems of high cost and air pollution that take place while recycling, so many researches about degradable plastic to solve above-mentioned problems fundamentally are on being developed actively at all the countries over the world.
The technology concerned with degradable plastic can be classified into three groups, i.e., photolysis technology, biodegradation technology and photo-biodegradation technology.
And the photolysis technology can be further classified into two types, i.e., introduction of photosensitive functional group and addition of photosensitive reagent. The types introducing photosensitive functional group were developed by the Dow Chemical Company which commercializes a copolymer of ethylene with carbon monoxide, and by Union Carbide Corporation, and by Bayer Corporation. And, the type adding metal complex compound developed by Scott-Gilead was a main stream of the type adding photosensitive reagent, and Ampacet Corporation and Ideamasters Corporation also commercialized this type of material. But, these photolyzable products have problems in that the production cost is high, and when being buried in the soil, they couldn't be degraded because the sunlight is blocked and accordingly they cannot absorb the photo energy. Therefore, the plastic waste problem cannot be solved only by the photolysis technology, so researches about the biodegradation technology are continuously on being developed.
The biodegradable plastics comprise polymeric products of microorganism such as PHB(Poly-β-hydroxybutylate), polymers synthesized from the biochemicals produced by microorganisms and the natural polymer such as Chitin. But, these kinds of biodegradable plastics are not appropriate economically because the production cost is high, so the polymer wherein the starch and so forth is added into the general plastic was proposed.
U.S. Pat. No. 4,021,388 discloses a biodegradable plastic composition wherein the matrix resin and the starch are mixed. Further, U.S. Pat. Nos. 4,133,784 and 4,337,181 disclose methods for manufacturing biodegradable film by adding powdered starch into the ethylene-acrylic acid copolymer. But, these compositions have limitations on commercialization in that the production process becomes complicated and the production cost increases high because the starch or the modified starch is used for the biodegrading additives.